Tunable Proton Diffusion in NdNiO₃ Thin Films under Regulated Lattice Strains

Inspired by the discovery of proton-induced resistance switching in perovskite rare-earth nickelate (RNiO3) films, control of a phase transition via proton doping in strongly correlated systems is considered as a paradigm to explore emerging iontronics functions. Nevertheless, the microscopic proton dynamics under an intrinsic factor of RNiO3 films, namely, lattice strain, has not been clarified in detail. Here we systematically demonstrate a tunable proton diffusion within the perovskite lattice by regulating structural strain in NdNiO3 (NNO) films. The quantification of the proton dynamics, as well as the corresponding resistance modulation ratio (Rr) and proton diffusion coverage, is found to be significantly sensitive to the strain. Introducing +2.57% in-plane tensile strain into NNO leads to a suppressed proton diffusion, which ultimately results in a fairly small Rr of ∼102. In contrast, NNO film with an in-plane compressive strain of −0.03%, of which Rr is ∼106, shows a higher degree of proton diffusion. This finding, supported by results of a density functional theory calculation, reveals the role of lattice strain in controlling the proton diffusion in the RNiO3 system and, in a broader context, in designing multifunctional iontronics devices.